dividing perennials (and some shrubs): when, why and how-to, with ken druse

ONE OF MY favorite books by our friend Ken Druse is called “Making More Plants,” and though it’s about all kinds of propagation, Ken and I talked the other day about what is maybe the easiest way of all to make more plants, which is by dividing them (like the Trillium erectum rhizomes above).

In most of the country this spring 2020, we’re not out shopping at garden centers, browsing for new adoptees the way we usually would be. But maybe you, like Ken Druse and I, are ready to do some shopping in your own garden, looking for divisions of favorite things that would work elsewhere, or simply keeping that bee balm from overrunning everything else that shares the same bed with it. We discussed dividing plants—the how, the when, the why, and how even certain shrubs (not just herbaceous perennials) can be divided. Ken even made a step-by-step video for us of the process.

Plus: Comment in the box at the bottom of the page to enter to win a copy of Ken’s “Making  More Plants” book.

Read along as you listen to the April 13, 2020 edition of my public-radio show and podcast using the player below. You can subscribe to all future editions on Apple Podcasts (iTunes) or Spotify or Stitcher (and browse my archive of podcasts here).

dividing plants: when, why and how, with ken druse



Ken Druse: Hi, Margaret. It’s very sweet of you to recommend that old book, which is still available.

Margaret Roach: Yeah. No, it’s a good one because it’s technically expert but not daunting is the thing that I thought about it. It makes me feel like you’re there with me and you’re encouraging me. It’s that voice.

Ken: Good.

Margaret: Good. Do you remember the first plant you divided, Ken? I think mine was Siberian iris.

Ken: Thinking back, I kind of remember a European ginger in the old Brooklyn garden.

Margaret: Oh, yeah-

Ken: I want to hear about your iris, too.

Margaret: Well, I had made the garden when my mother was ill years ago like we talked about last time and I was in my 20s, I was just starting gardening. One of the things I planted was Siberian iris and then it was time, eventually, when she was too ill to stay home, it was time to sell the house and move on. I bought the house I’m in now, eventually, and I moved some of the plants from my first garden there at her house to here. And so I had to dig up this Siberian iris and take some of it with me and that was interesting because it’s a quite tough cookie underground. It’s not some gentle little thing. You just said European ginger, which isn’t like a rock underground. [Laughter.]

Ken: No.

Margaret: So that was the idea, and I looked in all the books and it said, “Oh, the center part may fade out, so you want to get rid of the center part, and you want to keep wedges from the ring around the dying-off center part.” Oh, my goodness. That was an education for me, my first experience with dividing.

Ken: Did you have a chainsaw?

Margaret: [Laughter.] I didn’t know about chainsaws then. I was a city girl.

Ken: Well, I remember the ginger because… I don’t know if you’ve ever done this, but you buy-

Margaret: I have.

Ken: You buy a gallon container of European ginger, which is a beautiful evergreen plant, and you want it to be a groundcover. And you plop it in the ground and it’s beautiful, but nothing happens. It doesn’t get any bigger, year after year after year and-

Margaret: It stays in this congested little shape of the pot that it used to be in. Yup, yup.

Ken: I remember unearthing it and prying it apart, which was incredibly easy, it almost falls apart, and then planting each piece individually about six inches apart and each piece became as big as the original. That’s one plant that I learned: “divide that plant.” Because just as we were saying, it stays in that little clump unless you intervene. [Above, Ken made a video in spring 2020 of dividing the ginger.]

Margaret: Well, I think a lot of those little woodland groundcovering things that grow in the shade, I think they adapt to growing among the roots of trees and shrubs, and they can go sideways gradually and so forth. But to be put in a plastic pot, you know what I mean, and it can’t go anywhere, and I just think it sort of grows together in this mat that’s quite unlike what it does in its natural habitat, and I’ve seen a lot of other little woodlanders… Speaking of woodlanders—and that’s a non-native thing is Asarum europaeum, the European ginger you were just talking about. It has shiny leaves kind of, what would you say, heart or kidney-shaped? I don’t know.

Ken: [Laughter.] Which organ? Kidney, maybe.

Margaret: Yeah, kidney-shaped evergreen leaves. But, speaking of a native one, you and I learned how to divide a native groundcover of the woodland. We learned it together and we’ve talked about it on the show before. You know I’m talking about Trillium, right?

Ken: It’s a miracle. [Laughter.]

Margaret: You’re right.

Ken: I don’t know. We’re giving it as advice even though it doesn’t make any sense. But we were told from somebody who had a thousand trillium that she divided her plants when they were in flower. And I can see the reason to do that, because you can see them because they’re ephemerals, and they disappear in the fall when you’d like to or think about dividing them, but she divided them in flower and so I did, too, and it works.

Margaret: Right. We would dig up—while they’re in flower, when you can see them—you’d kind of dig up this little creature and if it’s been growing for a while and there’s multiple stems, there will be sort of these little knobby rhizomes at the bottom of each stem, yes. Kind of tease those apart. [A spadeful of Trillium rhizome in Margaret’s garden, above, on their way to new locations. More on how to divide trillium.]

Ken: Well I think with Trillium you kind of cut them apart because it’s got like a little gnarly finger-shaped thing with a couple of points, which are the growing eyes, and you can snap them apart or cut them apart and plant each part. And then, actually with almost everything, you have to water and you have to keep up with watering unless there’s plenty of rain, but you want those plants to be well-established. And you can’t just plant them and forget them, even though they’re native plants; they need attention for the first year.

Margaret: Let’s backtrack for a minute. Dividing, so we’re talking about perennials so far, and perennials doesn’t mean permanent. Just because you plant something that is a perennial doesn’t mean you never have to do anything with it or lift out of the ground again. Although there are some cases where that’s true, like peonies, unless you want more of a particular one, you could probably leave them there for 50 years and they’ll just keep doing their thing.

But a lot of them do need some divisions. It’s kind of like, what are some of the reasons you would divide, and one was what you observed with that ginger. It wasn’t going anywhere on its own, and you were looking for it to sort of move around.

Ken: Yeah. I wanted a groundcover, not just one little round clump.

Margaret: And so other reasons might be I love what it’s doing over here with given plant, like we’re talking about with the trilliums, I want to make another group of trilliums over there. It might be to have more somewhere else as I called it in the intro, “shopping in your own garden.”

Ken: Or making it for a friend, because that’s one of the wonderful things about having plants is unlike some treasures, you can share them.

Margaret: [Laughter.] It might be to move it around, it might be to make it behave in a different way. I mentioned also in the intro, like the bee balm, the Monarda, some of these things if you don’t divide them, and keep them within a given territory, they’ll just run through a whole bed and overtake their neighbors. That’s another reason to have a tough hand with certain plants and take off pieces from sort of their perimeter.

Ken: And then what do you do with the pieces? I mean, Margaret. [Laughter.]

Margaret: You’re supposed to not necessarily look for a place for them unless you really have a place for them. You’re supposed to compost them, but whatever. And so other reasons to divide, something’s getting, I mentioned the Siberian iris at the beginning, and some things get like that, it becomes like a doughnut. Like the center of the doughnut is empty; an old Siberian iris and you have this ring around the outside that’s still flower.

Ken: Rejuvenation.

Margaret: Yeah, exactly. Those are some reasons, but then the when and how also varies. And it can be from you need to divide them every year, like perennial mums, which a lot of people don’t even know that there are perennial chrysanthemums, but there are. You have to divide them every year for them to really perform well. But some things, like I said with the peonies, not so much. You don’t want to disturb them, because you’ll interrupt the flowering cycle. What are some of the things that you divide a lot, a little, or are you on a campaign right now since we’re home bound? Are you doing a lot more dividing than usual? [Laughter.] [Above, Margaret’s two favorite perennial mums, ‘Sheffield Pink,’ left, and ‘Will’s Wonderful.’]

Ken: Well, I actually did some ginger just like we were talking about, some European ginger, because the American one is just fine moving around by itself.

But it’s interesting that you mentioned chrysanthemum, because probably a lot of people that bought chrysanthemums in the fall at the gas station [laughter] or something and plant them, and they don’t come back in the spring because, unlike a lot of things, they don’t want to be fall-planted. They want to be spring-planted, but they’re usually not available in the spring. If you have some growing that you once bought in the spring, that’s important to do that in the spring, to do that division in the spring and not disturb them in the fall, for us, because they’re not incredibly hardy in Zones, let’s say for example, 6, 5, 4, they might live, but they don’t want to be disturbed. That’s one thing.

You mentioned Iris and Monarda. You’re mentioning good plants to divide, I hadn’t thought about it. Well you’re talking about rejuvenation and good health and things like that, but I always think about making more plants, and the biggest reason for me to divide plants as you said, is to have more of them.

And I remember dividing—if you can call it dividing—lilac shrubs because sometimes lilacs, they often have water sprouts, or they have some shoot that comes up even it can come up in the path. And that’s an opportunity to get another plant and maybe talk a friend into giving you another plant.

Years ago I got a wonderful semi-double white lilac from our dear friend, the late John Trexler. And in the winter with snow I had a spade, and I dug straight down because I figured it had a runner, and it did. And I lifted that plant and wrapped in moist newspaper in Massachusetts and drove it to actually the new garden in New Jersey, which that’s 20-something years ago. Sorry to interrupt myself and you.


Margaret: No, not at all because you’re absolutely right. I have a mock orange, a gold-leaf mock orange, an old-fashioned shrub. It’s a kind of messy thing. It needs to be cleaned up; it gets twiggy and nasty. But it still has that incredible … those white flowers that are so fragrant in the spring, and this is a gold-leaf one. It looks nice all the time during the season and that’ll sort of send off like babies to the side, you know when you can kind of dig one out that’s-

Ken: And send it to me.

Margaret: And send it to you. O.K. actually, I will then. I will. And hydrangeas sometimes. Have you had that happen with hydrangeas, like that they sort of … like a little piece might lie down and layer, or certain things will root? I’ve just had things sort of next to mom, next to the parent plant that I think have kind of rooted. [Above, Margaret’s Philadelphus coronarius ‘Aureus.‘]

Ken: And sometimes you can do that, you can make that happen.

Margaret: Yeah. Making more plants.

Ken: [Laughter.]

Margaret: So you mean bending down-

Ken: Bend down the branch if it’s close to the ground, let’s say like a Hydrangea quercifolia, the oakleaf hydrangea. And you damage it a little bit either by pushing it down pretty hard or cutting it, nicking it with a knife and put that part a little bit under the soil and put a rock on it, and then forget about it for two years and come back and cut it off, and you’ve got an all new shrub for another place or to give to someone because you love it.

Margaret: So layering as a way to make more plans and then divide it and then divide it off from the parent plant.

Ken: If you picture something, if you’ve ever grown a strawberry, an edible strawberry, they send out these runners that start new plants and so you’re dividing in a way, but you’re just cutting off the runner and the new plant, and moving it and having a fresh new plant that’s going to bear fruit even more.

Margaret: Let’s talk a little bit about the when. I mentioned the mums and you were talking about the mums and the when: So give me some examples of how you figure out if it’s time. You just said you were moving the ginger. We both said we moved trilliums when they’re in flower, not that you can’t do it at another time. What are some other when considerations?

Ken: As a kind of general rule, if you’ve got a plant that blooms early in the spring, like a lungwort, like I, then you want to move that either before it comes up or when it’s just starting to show. Those early flowering things: You’ve got to move them early and it’s even getting, well it is, it’s too late for a lot of them. I mean you can move them, but if you really want the greatest success and flowering and vigor, you want to do them early.

But things that bloom later, like garden phlox, they’re probably just coming up, and you can move them now or for the next few weeks, because they’re summer-blooming. That’s my general rule. If it’s early blooming, move it early—or in the fall if it’s a very hardy plant. And for summer-blooming things, you can move them in the fall, too, but you can also move them a little bit later [in spring].

And I’ve moved some plants or divided some plants that were already 18 inches tall. The Korean aster, Kalimeris, and I cut those back, cut them in half, and then dug them—it’s a very vigorous plant—and move that.

And the hostas are just showing the points of the hostas, so they have to be moved when those points are about just coming up between half-inch and an inch before they start to turn into leaves. I have a serrated knife that’s dedicated to the garden and not to the kitchen, and I cut in between the eyes or those points and sometimes I’ll cut right in the ground while they’re still in the ground. And then take a spade and lift part of the clump and move it to another place.

As I’m saying all these things, I’m thinking all these opportunities for symmetry, to move half of the plant across the path and have two plants that are paired to introduce the path. Sounds good. [Above, Margaret’s favorite lungwort, Pulmonaria rubra.]

Margaret: You just mentioned serrated knife. I have my former bread knife from many years ago is in my garden bucket, you know my tool bucket, so definitely a must tool. And you don’t need a fancy thing that you buy special, I mean literally it can be an old serrated knife for cutting up some of these root systems.

Now and you just mentioned various things, the lungwort, the Pulmonaria and so forth, and when to move them or and the hostas, for instance. Now, I have a friend who says, “When’s a good time to do something? When you have time.” Because sometimes we get too busy and we miss the chance of the ideal time. It doesn’t mean you’d kill a hosta if you lifted it and cut it up in leaf, it will look messy this season. Do you know what I mean? Or it doesn’t mean that you’ll kill the Pulmonaria. Just so people don’t worry. It won’t kill it if you move it after it flowers, probably. But do you know what I mean? It’s not ideal, but sometimes it’s the only time and we understand that. We’re not saying “or else” in most of these cases.

Ken: Well as you’re saying that, sometimes you’re in a place where you have to rescue a plant for some reason-

Margaret: Right, exactly.

Ken: And you just have to do it when you can do it. But if I’m digging or dividing a plant at the not-perfect time, for example, in the summer when it’s hot, but it has to be done, I always think: How much of the roots am I losing? And then I try to trim the plant on top to be equal to the amount of root loss. To compensate for the root loss, I’ll reduce the foliage loss … well, I’ll make the foliage loss. Otherwise, it’s going to wilt, and it’s going to take so long to recover if it even lives. But if you cut the plant back and sort of equal the root loss, the giant disturbance, then you have a much better chance. And again: water, water, water.

Margaret: There are some things, like I was thinking of another one of my early escapades. Early on I had tried to grow bearded iris, and unlike the Siberian iris, so they have a very different root structure. They’re like those fleshy rhizomes, and they’re almost above the surface kind of looking. People probably know what I’m talking about. And those are one where I wouldn’t move them at any old time. I’d probably do that in like July, August after they were done flowering. Does that make sense to you?

Ken: That’s exactly correct. [Ken’s 2010 video of dividing bearded iris, above.]

Margaret: And just because of that fleshy thing and it’s going through this big… Anyway, it puts a lot of energy into getting ready to do its flowering thing and I’d wait until it was done with that.

Ken: They’re semi-dormant. That’s another time, just like in the fall for hardy plants, and with iris you do want to move them when they have a little quiet moment in mid- to late summer and then sometimes they put on a little more growth in the late summer. You do want to do it when they’re quiet. And with bearded iris, you have to divide them. Not every year, probably every third year, second or third year, because they take a little while to re-establish, but they need to be rejuvenated. They need it. Some plants do.

Margaret: Visualizing those, also brings up the fact that when we go to lift a plant… The other day I was cleaning up a bed and I lifted a little bit of the Japanese forest grass, Hakonechloa macra, I have the ‘All Gold’ type, nice semi-shade, low, graceful grass, groundcovering kind of thing. And the root system of that is, it looks like, I don’t know [laughter], someone stuck their finger in an electric socket or something. It’s like “boing!”, it’s this crazy, wire-y, woody… but you can’t really tell where the crown is, the center. Do you know what I mean? It’s just kind of a crazy-looking thing. I should take a picture of a piece to accompany the transcript of the show.

And you talked about how you could just with your fingers tease apart those European gingers once you lifted it, and that was easy. Now, we just talked about the bearded iris and we can lift those, but some things are kind of like a big, thick mass and other things are like fleshy, like daylilies, underground and do you know what I mean? Do you have an approach for what you do when you then see the root structure of something? We said “knife” in some cases. [Above, a piece of the uprooted Hakonechloa root system; you an see a couple of point pink growth points.]

Ken: Knife, yeah. And so many books show back-to-back garden forks and you stick it in and pry them apart. I always found, for example, the Siberian Iris, you just damage so much of it doing it that way. In general, I don’t do that. I’ll dig up the entire clump with soil, and then get my serrated knife again, especially in the case of something like Hakonechloa, you can’t generalize for all grasses. I’ll interrupt myself. One thing about all of those Asian grasses is they’re kind of late-season things. The timing is important, and that would be something that you might divide now because they’re really just getting started and some of those big grasses, you need a backhoe to divide them when they get older [laughter].

Margaret: Well, many years ago I was given by the person who used to be in charge of the gardens at Rockefeller Center, the so-called Channel Gardens, Dave Murbach. You remember Dave, of course. And one time he told me, he said, “You have a pickup truck, don’t you Margaret?” This is when I worked in Manhattan, and this is 25-plus years ago. And I said, “Yes, I do.” And he said, “Well, we’re getting rid of the grass garden installation, if you want some divisions…”—he used the word divisions—”…of some grasses? You could take some clumps.”

And I’m thinking, “Oh, how sweet, when I’m leaving Friday for upstate.” Well, the guys were there at the door [laughter], at the driveway of Rockefeller Center. They were there with like 40,000 tons of… these giant clumps because to take them out of the ground you need, like you say, heavy equipment because they’re really woody underground.

In the last few minutes, any other sort of tips, things you’re encountering that you want to make sure to share or whatever about division?

Ken: Well, you know what hens and chicks are, or hen and chicks, Sempervivum, they’re succulents and they look kind of like Echeveria, they’re rosettes. And they’re called hen and chicks because there’s a main plant, and surrounding the main plant are little baby plants. And you can just divide those by just pulling them off and planting them individually. That’s almost a self-dividing plant, wouldn’t you say?

Margaret: Right. It sends off the baby a little bit of distance away. Yeah. And you could take advantage of that.

Ken: And whenever I talk to you, I get so excited, and then I run out to the garden and start doing it. I’m going to get my knife [laughter] and head out there and make more plants.

Margaret: And I just think again, when you make more plants, if you’re not going to compost them, if you’re going to want to reuse them, maybe before you dig up a hundred things and have a tarp full of creatures that are uprooted, think about where they’re going to go-

Ken: Oh, boy.

Margaret: Because that’s my thing is I’ll get really excited and I’ll start, “Oh, I’m going to divide this, and I’m going to take off a piece of this because it’s going too far to the left or too…” And then suddenly, I have this tarp full of goodies, but I haven’t thought through what I’m going to do next. And they don’t love to be out of the ground. Sometimes I’ll just heel them in in an empty vegetable bed, and water them in and keep them in better condition until I can use them later on. But making a plan, I think, is not a bad idea.

Ken: Right. Know where you’re going to put them, even if you’re going to put them in a pot to give to a friend. Keep those roots out of sunlight, and maybe cover them with burlap or moist newspaper or something and put him in the shade, while you’re transporting them and then when you plant them, water and keep your eye on it and water them well because you want to help them get established.

Margaret: So Ken, maybe we’ll have a giveaway with the transcript of this show for “Making More Plants,” your propagation book that I love so much and it’s good as always to speak to you. I miss you. I know, I miss you. So anyway, we’ll talk about that off the air. [Laughter.]

Ken: I’m always here for you.

Margaret: O.K. All right. Talk to you soon.

Ken: Be safe.

Margaret: You, too.

enter to win ken’s ‘making more plants’

I’LL BUY A COPY of “Making More Plants: The Science, Art, and Joy of Propagation” by Ken Druse for one lucky reader. (That’s the paperback cover, above; the hardcover edition cover is up higher on the page.) All you have to do to enter is answer this question in the comments box at the very bottom of the page:

What are you dividing this spring–or later in the season–and what’s your reason for doing so in this case?

No answer, or feeling shy? Just say something like “count me in” and I will, but a reply is even better. I’ll pick a random winner after entries close at midnight Tuesday, April 21, 2020. Good luck to all.

(Disclosure: As an Amazon Associate I earn from qualifying purchases.)


prefer the podcast version of the show?

MY WEEKLY public-radio show, rated a “top-5 garden podcast” by “The Guardian” newspaper in the UK, began its 11th year in March 2020. In 2016, the show won three silver medals for excellence from the Garden Writers Association. It’s produced at Robin Hood Radio, the smallest NPR station in the nation. Listen locally in the Hudson Valley (NY)-Berkshires (MA)-Litchfield Hills (CT) Mondays at 8:30 AM Eastern, rerun at 8:30 Saturdays. Or play the April 13, 2020 show using the player near the top of this transcript. You can subscribe to all future editions on iTunes/Apple Podcasts or Spotify or Stitcher (and browse my archive of podcasts here).

  1. Martha Gioumousis says:

    I’m digging and dividing echinacea and hellebore for gardening friends this week.
    And moving some trillium, primroses, astilbe, heuchera and winter aconite where a maple tree has to come down (boo hoo), so will divide them, too.

  2. Kathy Crown says:

    I’ll be dividing iris soon and Monarda sooner. The iris are ready (circling) and the Monarda got heeled into a veggie bed and promptly took over – great for pollinators, but…
    I’d *love* a copy of Ken’s book :)

  3. Marian Henneman says:

    I’m dividing Kalimeris and following Ken’s advice to cut the transplant back by half. Thanks, Ken.

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